1. Field of the Invention
The present invention relates to a protective layer transfer sheet and a print. More particularly, the present invention relates to a protective layer transfer sheet which can impart excellent fastness properties to an image in a print comprising a substrate having thereon the image, and a print having an image possessing excellent fastness properties.
2. Background Art
Halftone images and monotone images, such as letters and symbols, have hitherto been formed on a substrate by thermal transfer. Thermal transfer methods widely used in the art are thermal dye transfer and thermal ink transfer.
The thermal dye transfer is a method which comprises the steps of: providing a thermal transfer sheet comprising a substrate sheet bearing a dye layer formed of a sublimable dye as a colorant melted or dispersed in a binder resin; putting this thermal transfer sheet on the top of a substrate (optionally having a dye-receptive layer); applying energy corresponding to image information to a heating device, such as a thermal head, to transfer the sublimable dye contained in the dye layer in the thermal transfer sheet onto the substrate, thereby forming an image.
For the thermal dye transfer, the amount of the dye to be transferred can be regulated dot by dot by regulating the quantity of energy applied to the thermal transfer sheet. Therefore, excellent halftone images can be obtained. In this method, however, unlike the formation of an image by a conventional printing ink using a pigment as the colorant, a relatively low-molecular weight dye is used as the colorant, and, in addition, a vehicle is absent. For this reason, the formed image is disadvantageously poor in fastness properties, such as light fastness, weather fastness, and rubbing fastness.
A known method for solving the above drawback is to use a protective layer transfer sheet and transfer a protective layer containing an ultraviolet absorber or the like onto the formed image. The light fastness of the image can be improved to some extent by this method. However, the extent of the improvement is still unsatisfactory. Cyan dyes are particularly likely to fade. Therefore, light irradiation leads to a lowering in density of the image and, at the same time, causes a change in hue to red, resulting in remarkably deteriorated image quality.
Another problem involved in the conventional protective layer transfer sheet is that kick back is likely to be created. The kick back refers to such a phenomenon that, in the course of production of an integral transfer sheet, comprising protective layers and dye layers provided in a face serial manner on a common substrate sheet, involving a plurality of times of winding and rewinding, for example, the steps of rewinding the protective layer and the dye layer after coating, such as winding after the completion of coating, winding at the time of slittering after the coating, and winding around a bobbin as a form of a product, during storage in a wound state until next steps, the dye is first transferred (kicked) from the dye layer onto the backside of the substrate sheet, and, at the time of rewinding in the next step, the kicked dye is retransferred (backed) onto the front side of the substrate sheet facing the kicked dye. Rolls prepared in respective steps are different from one another in opposed faces. This creates a problem wherein each color dye is transferred onto the surface of the protective layer by the kick back phenomenon.
The creation of the kick back phenomenon in the transparent protective layer leads to a problem that transfer of the protective layer onto an image causes the image to be colored with the dye transferred by the kick back phenomenon, resulting in remarkably deteriorated image quality.
A further problem involved in the conventional protective layer transfer sheet is as follows. When transfer of only a smaller portion than the protective layer region in the protective layer transfer sheet onto a receptive sheet in its predetermined protective layer forming portion is contemplated, the protective layer is excessively transferred, that is, a larger portion than the contemplated portion of the protective layer in the protective layer transfer sheet is transferred. This creates the presence of an extra transferred protective layer portion not adhered to the receive layer, that is, an edge, on the outer periphery of a protective layer transferred onto the predetermined protective layer forming portion. The edge comes off the protective layer within a printer, leading to contamination of the interior of the printer and poor appearance of the print.
The present invention has been made under the above circumstances, and it is an object of the present invention to provide a protective layer transfer sheet which has excellent transferability and which can impart fastness properties, especially remarkably enhanced light fastness, to images. It is another object of the present invention to provide a print having fastness properties enhanced by the protective layer transferred from the protective layer transfer sheet.
According to one aspect of the present invention, there is provided a protective layer transfer sheet comprising: a substrate sheet; and a thermally transferable protective layer provided on at least a part of one side of the substrate sheet, the protective layer comprising an alicyclic polyester resin prepared using an alicyclic compound as at least one of a diol component and an acid component.
According to a second aspect of the present invention, there is provided a protective layer transfer sheet comprising: a substrate sheet; and a thermally transferable protective layer provided on at least a part of one side of the substrate sheet, the protective layer comprising a thermoplastic resin and an ultraviolet absorber, the ultraviolet absorber being a benzotriazole ultraviolet absorber represented by formula (2), the content of the ultraviolet absorber in the protective layer being 10 to 40% by weight: 
wherein X and Y each independently represent an optionally branched alkyl or aralkyl group having 4 to 10 carbon atoms and Z represents a hydrogen or chlorine atom.
Further, according to a further aspect of the present invention, there is provided a print comprising: a substrate; and, provided on at least one side of the substrate, a dye image and a protective layer covering at least a part of the image, the protective layer having been formed by transfer from any one of the above protective layer transfer sheets.
In the protective layer transfer sheet according to the first aspect of the present invention, the alicyclic polyester resin imparts excellent light fastness and good transferability [a capability of being faithfully transferred onto a predetermined protective layer forming region (that is, a predetermined region on which the protective layer is to be transferred; this region being hereinafter often referred to as xe2x80x9cpredetermined transfer portionxe2x80x9d) in a receptive sheet] to the protective layer, and the protective layer in the protective layer transfer sheet is much less likely to create kick back. Transfer of this protective layer onto images can prevent dyes constituting the images from being faded by light and thus can impart excellent light fastness to printed images.
In the protective layer transfer sheet according to the second aspect of the present invention, the protective layer has excellent ultraviolet absorption. Transfer of this protective layer onto images can prevent dyes constituting the images from being faded by light and thus can impart excellent light fastness to printed images.